Interpretive Summary: Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is a widespread pest that can reduce the yields of soybean. Growing SCN-resistant soybean varieties in fields infested with SCN can improve yield, but the impact of SCN on seed quality of lines with modified seed composition is unknown. A study was conducted to determine if SCN resistant or susceptible rootstock had an impact on the seed composition of soybean lines that had been developed to produce modified levels of unsaturated fatty acids (FA); high oleic acid and low linolenic acid are desirable FA levels for soybean seed. In this study soybean lines developed for modified FA levels were grafted onto other soybean lines that were bred to be either resistant to SCN or susceptible to SCN; a mid-oleic line and a low linolenic line were compared to other conventional soybean lines. Both grafted and non-grafted plants were grown in a SCN infested field. The analysis of harvested seeds for FA levels of the modified lines revealed that 1.) the mid-oleic line produced more oleic acid when grafted onto the SCN resistant rootstock than when grafted onto SCN susceptible rootstock but 2.) linolenic acid production of the low linolenic line was not different when grafted onto the SCN resistant or SCN susceptible rootstock. The significance of this research is that SCN can impact the expression of seed quality and that soybean lines bred for modified fatty acid levels in seed and resistance to SCN should be used where SCN infestations are evident. This information will be important to soybean researchers in their attempts to design more tolerant crop plants using classical breeding or biotechnology.

Technical Abstract:
Growing soybean cyst nematode (SCN, Heterodera glycines Ichinohe) resistant varieties in fields infested with SCN can improve yield, but the impact of SCN on seed quality of lines with modified seed composition is unknown. The objective of this study was to determine if SCN resistant or susceptible rootstock influenced the composition of the seed of soybean lines developed for unsaturated fatty acids (FA) differences. Five soybean lines with modified or normal levels of fatty acids were Y-grafted to generate a 5X5 combination of plants with a SCN susceptible or resistant rootstock having a self-grafted branch, a scion (alien) grafted branch, or non-grafted branch. Control plants were not grafted. In 2004 and 2005 all plants were randomly transplanted into field plots verified to be infested with SCN Race 3 and planted with Asgrow line 3302 (SCN susceptible) or Asgrow 3701 (SCN resistance to Race 3 derived from PI-88788). Seeds were harvested at physiologic maturity (R8) in 2004 and 2005 and analyzed for five unsaturated fatty acids. Seed oleic acid of the mid-oleic line S03-1379-2 were significantly greater than controls when grafted onto the SCN resistant line S97-6946 than when grafted onto SCN susceptible lines Williams 82 or Magellan. Seed linolenic acid of controls for the low linolenic line IA-3017 were not different than when grafted onto S97-6946, Williams 82, or Magellan. FA levels of the seed from reciprocally grafted S97-6946, Williams 82 and Magellan were not significantly different from their controls. SCN can impact the expression of seed quality of soybean lines bred for modified FA levels in seed and lines with resistance to SCN should be grown where SCN infestations are evident.